In video coding systems, spatial and temporal redundancy is exploited using spatial and temporal prediction to reduce the information to be transmitted. The spatial and temporal prediction utilizes decoded pixels from the same picture and reference pictures respectively to form prediction for current pixels to be coded. In a conventional coding system, side information associated with spatial and temporal prediction may have to be transmitted, which will take up some bandwidth of the compressed video data. The transmission of motion vectors for temporal prediction may require a noticeable portion of the compressed video data, particularly in low-bitrate applications. To further reduce the bitrate associated with motion vectors, a technique called Motion Vector Prediction (MVP) has been used in the field of video coding in recent years. The MVP technique exploits the statistic redundancy among neighboring motion vectors spatially and temporally.
In HEVC development, a technique named Advanced Motion Vector Prediction (AMVP) is currently being considered. The AMVP technique uses explicit predictor signaling to indicate the MVP candidate selected from a MVP candidate set. The MVP candidate set includes spatial MVP candidates as well as temporal candidates, where the spatial MVP candidates include three candidates selected from three respective neighboring groups of the current block. The MVP candidate set proposed for the AMVP also includes the median of the three spatial candidates and a temporal MVP candidate. The AMVP technique only considers the MV (motion vector) with the same reference picture list and the same reference picture index as the current block as an available spatial MVP candidate. If the MV with the same reference picture list and the same reference picture index is not available, the AMVP technique looks for available motion vector from the next neighboring block in the group. It is very desirable to develop a MVP scheme that can improve the availability of the MVP candidate of the neighboring block. The improved MVP scheme may cause smaller motion vector residues and consequently the coding efficiency can be improved. Furthermore, it is desirable that the MVP scheme will allow the predictor to be derived at the decoder based on decoded information so that no additional side information has to be transmitted.